By 1943-6 the standard light AA armament
had increased to 5x2 40mm and 7x1 20mm guns. Radar was also upgraded
to SG surface search
radar by this time.

At war's end, the ships were refitting with
kamikaze armament of 3x2,
2x4 40mm
and 3x1, 4x2 20mm with removal of one bank of torpedo tubes. The quad
40mm mounts also had improved fire control in the form of Mark 63 blind fire directors.

Three of the ships were completed with
fewer guns and one bank of
torpedoes to make room for an aircraft catapult for an OS2U Kingfisher.
This experiment was unsuccessful. The catapult could not turn a full
circle and the seaplane had to be launched to starboard and recovered to
port with the ship hove to, making it vulnerable to submarine attack.

The Fletchers,
completed in 1942-45, were the
wartime American
destroyers. Produced in
great numbers, they proved to be a sound design, and became perhaps the most successful of all American destroyer classes. The antiaircraft battery was
initially quite weak for a ship of this size, but it was greatly
improved
as the war progressed. The flush
decks gave
great structural strength, though at the expense of wet bows. The ships
were
tough, well-armed, and reliable, with good cruising range. On
the other
hand, they were not particularly fast for destroyers and lacked
somewhat in
maneuverability. As designed, they were much less top-heavy than
their
predecessors, but by war’s end the Navy had dumped enough
additional equipment
on board to reverse this departure from tradition.

They were the first U.S. destroyers designed after
the lapse of the
naval disarmament treaties, and the design process took almost two
years. The designers originally envisioned relatively small ships, not
more than 1600 tons, so that they could be build in greater numbers.
The debate over whether torpedoes or guns were to be the
primary armament was resolved early in the design process in favor of a
balanced armament, and most of the subsequent increase in displacement
came from the decision to incorporate Special
Treatment Steel (STS)
plate as splinter protection around the bridge and machinery spaces.
The increase in displacement also meant that a heavier antiaircraft
battery could be accommodated, which was just as well, since even this
heavier battery proved inadequate and had to be upgraded during the war.

Subdivision was good, with alternating engine and
fire rooms for greater machinery dispersion. Construction was
all-welded and all decks and the upper hull were of STS, with a
thickness of 0.5" (13mm) for the main deck and 0.75"
(19mm) for the upper hull. This gave a measure of protection from
splinters from near misses. Other portions of the hull and the lower
decks were thinner.

The machinery consisted of cruise, high-pressure,
and low-pressure turbines, with astern blading incorporated in the
low-pressure turbine. The boilers incorporated superheaters and
produced steam at 565 psi (3900 kPa) at 850 degrees Fahrenheit (454
degrees Centigrade).

Other improvements to the class included
sophisticated radar
plotting rooms (ancestors of the modern CIC) and
improved antisubmarine
gear. The original closed pilot house was replaced in late production
units with an open bridge that gave improved all-around vision, which
had proven important under air attack. The deck house, as originally designed, was made of lightweight aluminum alloy, but in later units this was replaced by steel due to the shortage of aluminum.

One notable weakness of the class was its poor
maneuverability, and it was claimed that even an Iowa-classbattleship could out turn a Fletcher. Subsequent destroyer
classes adopted twin rudders to improve the turning radius.

The timing of the new design was fortuitous.
Friedman (2004) notes that "the 'iron law' of mobilization is that only
equipment already in production can pass into mass production, and the
design of the Fletcher
coincided with the great acceleration of U.S. naval shipbuilding just
prior to and early in World War II." Thus the U.S. Navy was poised to
mass produce a sound, modern destroyer design for the greatest naval
conflict in its history. And mass-produced it was: 175 Fletchers were
completed, more than any other destroyer class, and the great majority
served exclusively in the Pacific.Construction took place at 11 different shipyards, include Bath-San Francisco, Bath-San Pedro, Bremerton, and Seattle-Tacoma.